Yves, I cannot compute PSI or bar. I understand the figures, but not relatively. I do it the old way, get the piston to TDC on the compression stroke (so valves are closed), lean the bike over so the spark plug thread is vertical, then carefully measure how much oil it takes to filll the combustion chamber, using a syringe.
I was taught to fill to the second thread to compensate for the hollow around the plug electrode (a minor detail really).
Then you simply calculate your static CR thus (combustion chamber volume + swept volume) / combustion chamber volume.
It’s a bit of a faff, but it’s the only way I know of to get a dependable figure.
For reference, my 850 runs 10.5:1 on pump fuel without issue. I put this down to the good combustion chamber shape and effective squish band effect.
Personally, I wouldn’t go to so much effort just to make such a small change! I’d put it on the list of things to do for next winter. But I guess I’m just showing how much lazier I am than you!!